From 24d69c5452ae1f4fcc89dc637fe94a92d39ef5a3 Mon Sep 17 00:00:00 2001
From: Yanming Zhou <zhouyanming@gmail.com>
Date: Wed, 1 Dec 2021 10:47:15 +0800
Subject: [PATCH] Optimize SimpleJpaRepository.exists(Example) for better
 performance.

1. Set max results to 1 to avoid full scan
2. Select 1 to reduce size of ResultSet

Original pull request #2368
---
 .../data/jpa/repository/support/SimpleJpaRepository.java  | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/main/java/org/springframework/data/jpa/repository/support/SimpleJpaRepository.java b/src/main/java/org/springframework/data/jpa/repository/support/SimpleJpaRepository.java
index f5f2fe1ef..adfc5e76b 100644
--- a/src/main/java/org/springframework/data/jpa/repository/support/SimpleJpaRepository.java
+++ b/src/main/java/org/springframework/data/jpa/repository/support/SimpleJpaRepository.java
@@ -530,8 +530,12 @@ public class SimpleJpaRepository<T, ID> implements JpaRepositoryImplementation<T
 	 */
 	@Override
 	public <S extends T> boolean exists(Example<S> example) {
-		return !getQuery(new ExampleSpecification<S>(example, escapeCharacter), example.getProbeType(), Sort.unsorted())
-				.getResultList().isEmpty();
+		Specification<S> spec = new ExampleSpecification<>(example, this.escapeCharacter);
+		CriteriaQuery<Integer> cq = this.em.getCriteriaBuilder().createQuery(Integer.class);
+		cq.select(this.em.getCriteriaBuilder().literal(1));
+		applySpecificationToCriteria(spec, example.getProbeType(), cq);
+		TypedQuery<Integer> query = applyRepositoryMethodMetadata(this.em.createQuery(cq));
+		return query.setMaxResults(1).getSingleResult() != null;
 	}
 
 	/*